Lunar and Planetary Science XXXVI (2005) 1196.pdf

NEW ACTIVE REMOTE-SENSING CAPABILITIES: LASER ABLATION SPECTROMETER AND LIDAR ATMOSPHERIC SPECIES PROFILE MEASUREMENTS. R. J. De Young and J. T. Bergstralh, Science Directorate, NASA Langley Research Center, MS 401A, Hampton, VA 23681, [email protected], [email protected]

Introduction: With the quality (M2 = 1.5). As tested, this anticipated development of high- system occupies a volume of 114 x 152 capacity fission power and electric x 45 cm, but it could be made propulsion for deep-space missions, it substantially smaller for space will become possible to propose applications. This laser could be the experiments that demand higher power pump source for the following than current technologies (e.g. instruments. radioisotope power sources) provide. Laser Ablation Mass Jupiter Icy Moons Orbiter (JIMO), the Spectrometer: High-energy pulses from first mission in the Project Prometheus the Yb:YAG laser, focused by a 2 meter program, will explore the icy moons of diameter transmission mirror, would Jupiter with a suite of high-capability produce energy densities of the order of experiments that take advantage of the 109 Watts cm-2 on a surface at a distance high power levels (and indirectly, the of 100 km. The resulting plasma would high data rates) that fission power generate ions of sufficient energy and affords. This abstract describes two quantity to be detected with a mass high-capability active-remote-sensing spectrometer on the spacecraft [1,2]. experiments that will be logical This would make it possible to map with candidates for subsequent Prometheus- very high spatial resolution the class missions. elemental compositions of the surfaces High-Energy Laser Pump of planetary bodies without atmospheres. Source: Both experiments incorporate a Figure 1 shows an experimental example high-energy laser as a pump source. of a laser ablation mass spectrum taken High-energy laser pump sources are at 18 m with a Nd:YAG laser. currently being developed for military and for industrial processing purposes. From the standpoint of technical maturity, they could be reasonably proposed for space science missions in the near future. However, they are inefficient and consequently require the high power levels afforded by fission. An example is the Yb:YAG master oscillator power amplifier system developed by Raytheon under DARPA sponsorship. In this case, a 25 kW Fig 1. Laser ablation mass spectrum of breadboard laser was demonstrated at lunar stimulant from [1]. The table list 1029 nm with efficiency of ten percent. the manufactures measured The laser system’s Q-switched output is concentrations. 25 J per pulse and it has good beam Lunar and Planetary Science XXXVI (2005) 1196.pdf

by slightly tuning the wavelength of the Lidar Profiling of Atmospheric signal seed laser. The OPO/amplifier Species: The Yb:YAG laser can be would have to produce about 100 mJ per operated at almost any power level up to pulse to accomplish water vapor 25 kW. Thus, this laser could also be measurements from Mars orbit. used to pump an optical parametric A Mission Scenario: The same oscillator/amplifier (OPO) to produce Yb:YAG laser used to pump a DIAL single-frequency pulses for a differential experiment could also be used ablate the absorption lidar (DIAL) experiment, to surface of an airless moon. Combining a measure the atmospheric abundance of laser ablation mass spectrometer and a almost any molecular species of interest. DIAL lidar in one package would For example, there have been provide a potent capability for several recent reports of detection of investigating planetary systems, methane in the martian atmosphere including atmospheres, rings, and [3,4,5]. Methane has a short lifetime satellite surfaces. (~350 yr) in the martian atmosphere, so References: [1] De Young R.J. some source must replenish it. This is and Situ W. (1994) Appl. Spectro., 48, potentially important because methane 1297-1306. [2] Situ W. and De Young can be produced by biological processes R.J. (1995) Appl. Spectro., 49, 791-797. as well as by non-biological processes. [3] Formisano V., Atreya S., Encrenaz A DIAL experiment in orbit around T.,Ignatiev N., Giuranna M.(2004) Mars could detect small variations in Science, 306, 1758-1761. [4] methane concentration near the surface, Krasnopolsky V.A., Maillard J.P., Owen giving clues to its source(s). The OPO T.C. (2004) Icarus 172, 537-547. [5] would be pumped at 1029 nm. For the Mumma M.J., Novak R.E., DiSanti on-line DIAL wavelength, a signal seed M.A., Bonev B.P., Dello Russo N., laser would generate pulses at 1.5 (2004) Bull. Am. Astro. Soc. 36, 1127. micron that would result in an idler wavelength of 3.3 microns (i.e. the wavelength of the strong methane ν3 fundamental). The off-line DIAL wavelength would be generated by slightly changing the signal seed laser wavelength. Another important problem is the distribution of water vapor in the martian atmosphere. This could be investigated with high sensitivity using the DIAL technique. In this case, the OPO would

be pumped by a frequency-doubled Yb:YAG laser at 514.5 nm. For the on- line wavelength, a signal seed laser at 1128 nm would result in an idler output of 946 nm (the wavelength of a strong water vapor absorption line). Again, the off-line wavelength could be generated